This invention relates to a method for preparing a (meth)acrylic acid ester. More detailedly, this invention relates to an improvement in a method for preparing a (meth)acrylic acid ester comprising an esterification step for carrying out esterification reaction between (meth)acrylic acid and an alcohol, and a separation-purification step comprising an acid-separating column, a low boiling matter-separating column and a rectification column for separating and purifying the (meth)acrylic acid ester from the (meth)acrylic acid ester-containing mixture obtained in the esterification step, and the improvement lies in circulating the bottom residue of the rectification column into the esterification step and/or the separation-purification step, and thereby effectively reusing the polymerization inhibitor still remaining in the bottom residue and efficiently recovering the (meth)acrylic acid ester still remaining in the bottom residue.
It is industrially carried out to prepare a (meth)acrylic acid ester by esterifying (meth)acrylic acid and the corresponding aliphatic alcohol having 1 to 4 carbon atoms in the presence of an acidic catalyst, and separating and purifying the (meth)acrylic acid ester from the resulting esterification reaction mixture.
As methods for separating and purifying the (meth)acrylic acid ester from the esterification reaction mixture, for example, a method for obtaining a highly pure (meth)acrylic acid ester by separating and purifying the (meth)acrylic acid ester using an apparatus composed of an alcohol-recovering column, a low boiling matter-separating column and a high boiling matter-separating column is described in Japanese Patent Publication No. 7-64787.
It goes without saying that it is industrially desirable to prepare a (meth)acrylic acid ester in a high yield and prepare a (meth)acrylic acid ester economically advantageously by reducing the preparation costs of the (meth)acrylic acid ester.
Therefore, the object of the invention lies in providing a method for preparing a (meth)acrylic acid ester in a high yield and economically advantageously.
The present inventors have re-examined the method described in the Japanese Patent Publication No. 7-64787, and as a result they have found that the polymerization inhibitor contained in the bottom residue of the high boiling matter-separating column in the method is not largely denatured, and therefore that the bottom residue can be reused by circulating it as such into the esterification step and the separation-purification step, and thereby that the (meth)acrylic acid ester can be obtained in a high yield. The invention was completed based on these findings. It is a discovery made for first time by the present inventors that the polymerization inhibitor contained in the bottom residue is not largely denatured.
Thus, according to the invention is provided in a method for preparing an (meth)acrylic acid ester comprising an esterification step for forming the (meth)acrylic acid ester by esterification reaction between (meth)acrylic acid and the corresponding aliphatic alcohol having 1 to 4 carbon atoms in the presence of an acidic catalyst, and a separation-purification step comprising an acid-separating column, a low boiling matter-separating column and a rectification column for separating and purifying the (meth)acrylic acid ester from the (meth)acrylic acid ester-containing mixture obtained in the esterification step, the improvement comprising circulating the bottom residue of the rectification column into the esterification step and/or the separation-purification step.
In the attached drawings, FIG. 1 is a flow sheet showing an embodiment of the method of the invention, and FIG. 2 is a flow sheet showing another embodiment.
In FIG. 1 and FIG. 2, 1, 2, 3, 4 and 5 show an esterifying reactor, an acid-separating column, a low boiling matter-separating column, a rectification column and high boiling matter-separating column, respectively.